1. Field of the Invention
The present invention relates to an image forming device, and more particularly, to an image forming device in which an image is formed by exposing an object with an exposure device in which an organic Electro-Luminescence (EL) element is used as a light-emitting element.
2. Description of the Related Art
An organic electric field light-emitting element that employs a fluorescent organic substance as a material for a light-emitting layer is referred to as an xe2x80x98organic Electro-Luminescence (EL) elementxe2x80x99. Since the organic EL element has such advantages that manufacturing thereof is more facilitated than other light-emitting elements and a thin and light weight light-emitting element can be formed, the organic EL element has conventionally been studied and developed as a thin type display element. In recent years, a high performance organic EL element, which is comparable with a light-emitting diode (LED) in terms of light-emitting luminance, light-emitting efficiency, durability, and the like, has been developed. Therefore, application has been studied of an organic EL element to an exposure head for exposing a photosensitive material such as a silver halide photosensitive material.
Typically, an organic compound layer comprises a transparent substrate, and an organic compound, and a pair of electrode layers (a cathode layer and an anode layer) for interposing the organic compound layer therebetween that are layered on the transparent substrate. The emitted light is outputted from the transparent substrate side. However, since the emitted light is a diffusing light source, and is also reflected from a surface of the transparent substrate, a problem is caused in that light outputting efficiency is low, thus making it difficult to obtain sufficient exposure amount.
Conversely, Japanese Patent Application Laid-Open (JP-A) No. 10-172756 discloses an organic EL light-emitting device in which a microlens is placed on the organic EL element between a light-emitting layer, and a light outputting surface of the transparent substrate so as to correspond to each other 1 to 1 to thereby improve the light outputting efficiency and increase light-emitting luminance in the direction of optical axis. Further, JP-A No. 11-354271 discloses a photosensitive material recording device in which an organic EL element array is formed on a substrate having a microlens to improve availability of the emitted light amount. Moreover, JP-A No. 2000-77188 discloses an exposure device and an image forming device in which an organic EL element array having microlens and an optical resonator structure is used, and wavelength at the light-emitting peak wavelength is put within a region of a half width of the sensitivity of a photosensitive member to improve availability of the emitted light amount.
However, when the area of aperture of the microlens is the same as that of a light-emitting portion of the organic EL element, a problem is caused in that the emitted light cannot be converged sufficiently, whereby an amount in which light is exposed becomes insufficient. Further, a problem is also caused in that, since the organic EL element is a diffusing light source, if the area of the microlens aperture and that of the light-emitting portion of the organic EL element are the same, crosstalk may occur. On the other hand, such problems can be solved by making the area of the microlens aperture larger than that of the light-emitting portion of the organic EL element. However, if the area of the microlens aperture is made larger, a problem is caused in that a layout space, i.e. a pixel pitch between the organic EL elements is extended, unexposed portions are produced on an object to be exposed, thus making it difficult to function the exposure device sufficiently.
In view of the aforementioned facts, an object of the present invention is to provide an image forming device in which the emitted light is highly available, optical crosstalk is minimized, and an image can be formed at high resolution.
In order to attain the aforementioned objects, an image forming device, comprising: an exposure section including a transparent substrate, a plurality of light-emitting elements that are arranged, with a predetermined gap disposed between mutually adjacent light-emitting elements, on the transparent substrate in a main-scanning direction and include light-emitting portions using an organic material, and microlenses formed on the transparent substrate in respective correspondence to each of the light-emitting elements and having an aperture diameter that is larger than the size of the light-emitting portion of each light-emitting elements, the emitted light from the light-emitting portions of the plurality of light-emitting elements being focused by the microlens to thereby expose an object to be exposed; and an exposure control section for moving the exposure section and the object to be exposed relative to one another, and dividing exposure corresponding to one main-scanning line into a plurality of exposures in order to fill a space between positions at which images are formed by the light-emitting portions of the organic EL elements that are adjacent to each other in the main-scanning direction.
In accordance with the image forming device according to the first aspect of the present invention, in the exposure device, the emitted light from a plurality of the light-emitting elements using organic materials which are arranged in the main-scanning direction is focused on the transparent substrate by the microlens that corresponds to each light-emitting element, whereby the object to be exposed is exposed. Further, the light-emitting elements are structured such that a transparent electrode layer for operating as an anode, a light-emitting layer that emits light by the voltage being applied thereto, and an electrode layer for operating as a cathode are layered on the transparent substrate by a vapor deposition or the like.
In this exposure device, the aperture diameter of the microlens is made to be larger than the size of the light-emitting portion of the light-emitting element, whereby availability of the emitted light can be increased, and optical crosstalk can be inhibited.
In this way, when the aperture of the microlens is made larger, an array pitch of one light-emitting element becomes larger, an unexposed space is produced between positions where the light-emitting portions adjacent to each other are focused, and image resolution is deteriorated. However, the amount of this deterioration can be compensated by the exposure controller such that the exposure device and the object to be exposed are moved relatively to each other in order to fill the space to be unexposed that is produced between positions where the light-emitting portions adjacent to each other in the main-scanning direction are focused, and exposure corresponding to one main-scanning line is conducted a plurality of times, whereby exposure at high resolution, i.e., image forming at high resolution is enabled.
In accordance with a second aspect of the present invention, in the above-described image forming device, in order to arrange microlenses so as not to overlap with each other, and carry out exposure corresponding to one main-scanning line a plurality of times without being duplicated, the array pitch of the light-emitting elements is at least twice or more the size of the light-emitting portion of the light-emitting element, and the aperture diameter of the microlens is equal to or less than the array pitch.
In accordance with a third aspect of the present invention, in the above-described image forming device, as the microlens, convex lenses formed at a light-emitting side of the transparent substrate, distribution refracting lenses formed inside the transparent substrate, or a combination of the convex lenses and the distribution refracting lenses are used.
In accordance with a fourth aspect of the present invention, in the above-described image forming device, since the exposure device comprises the plurality of row elements which are formed by arranging each of the light-emitting elements corresponding to mutually different colors and forms images corresponding to a plurality of colors at one time, an image corresponding to a plurality of colors can be exposed in an amount of time required for exposing one single color. Accordingly, color image formation at higher speed becomes possible.
In accordance with a fifth aspect of the present invention according to the fourth aspect of the present invention, since at least one row of the element rows is arranged such that it is offset in the main-scanning direction with respect to other element rows, the exposure device can be made compact.